10 DOROCIDARIS BLAKEI. 
Blakci in the shape of the plates of the abactinal system (PI. II. Fig. 17). 
The ocular plates are in contact with the extremities of the large anal plates 
inserted between the genital plates ; the other plates of the anal system are 
of a more uniform size than in tlie other species of the genus. In a s|)eci- 
men measuring 50 mm. in diameter, there ai-e 7-8 primary interambulacral 
plates ; these are covered by a comparatively coarse, irregularly arranged 
secondary granulation. The poriferous zone is somewhat flexuous, the fur- 
rows more distant, and the median ambulacral granulation finer, than in 
the other West India species of the genus. The ambulacral papilla? and 
those at the base of the primary radicles of D. Bartletii are nearly of uni- 
form size ; in D. papillata, those surrounding the radioles are somewhat 
larger, and in D. Blakci they are still more different, being comparatively 
much wider and flatter than the narrow ambulacral papillae. 
* Dorocidaris Blakei A. Ag. 
Dorocidaris Blakei A. Ag. Bull. M. C. Z., V., No. 9, p. 185, PI. IV., 1878. 
Dorocidaris Blakei A. Ag. Bull. M. C. Z., VIIL, No. 2, p. 70, 1880. 
Off Hiivima, 175-450 fathoms. 
Santa Cruz to Barbados, l(;3-27() fatboins. /G "3 - '''") ^ 
PI. /, PL n. Fly^. 1-1'>. 
This species (PI. I.) is perhaps the most interesting of the recent Cidarida3. 
Thus far the living Cidaridtc known have not shown any great or striking 
variety in the form of the radioles. With the exception of some of the 
recent species of the genus Gonioddaris, the radioles as a whole are charac- 
terized by their great uniformity, while among the fossils of the fixmily the 
great variation in the shape and size of the radioles of some of the Jurassic 
and Ci'etaceous species is most remarkable. In the description of species of 
the recent Cidaridae, it has not been unusual to lay great stress upon the 
differences noticed in the shape and ornamentation of the radioles. Com- 
parative studies of recent and fossil types have shown the practice to be 
dangerous, and the discovery of D. Blakii plainly pi'oves that hereafter we 
must proceed most cautiously in the determination of species from the char- 
acters of the radioles alone, no matter how strikingly they may appear to 
differ. Certainly, if the present species had been dredged without its two or 
three huge fan-shaped spines, it would have been unliesitatingly placed in the 
genus Dorocidaris, and been perhaps referred even to Z). pitpilhta, although 
there are differences in the coronal plates of the test and in the abactinal 
